Synthetic amino acids-derived peptides target Cryptococcus neoformans by inducing cell membrane disruption

We investigated synthetic amino acid-based approach to design short peptide-based antibiotics. Tautomerically restricted, amphiphilic 1-aryl-l-histidines along with hydrophobic tryptophan were utilized to synthesize the designed peptides. l-Trp-l-His(1-biphenyl)-NHBzl (12e, IC₅₀ = 1.91 μg/mL; MIC = 3.46 μg/mL) and l-His[1-(4-n-butylphenyl)]-l-Trp-l-His[1-(4-n-butylphenyl)]-NHBzl (16d, IC₅₀ = 1.36 μg/mL; MIC = 2.46 μg/mL) produced potency against Cryptococcus neoformans. Peptides with moderate antibacterial activities (IC_50s = 4.40-8.80 μg/mL) were also identified. The mechanism of action and cellular changes revealed that membrane disruption due to interactions of the positively charged peptides with the negatively charged membrane of the cryptococcal cells result in permeabilization, leading to pore formation. The internal localization of the peptides instigated the interactions with DNA causing fragmentation of the genetic material, which together with membrane disruption led to cell death. Flow cytometric analysis points to cells death by apoptotic pathway. Time kill kinetics and synergistic study confirmed the fungicidal nature and synergism with amphotericin B.